Not all suits are created equal, and it's the spot cards that often make the difference.
Here's an example.
Suppose you are in a spade contract. Which suit would you like to be playing with? Of course, that's a silly question. With the first suit, you will take five tricks even if partner is void in spades. You simply knock out the ♠ A and ♠ K and you have five tricks. With the second suit, you would be in dire straits if you had to play it opposite a void. You might end up taking only three tricks, two if you are really unlucky. Both suits have the same number of high-card points, but the spot cards in the second hand argue for caution, especially in competitive bidding, which will be covered in Chapter 5.
Suit quality is less of a consideration when opening the bidding, largely because in many cases you have no choice, as in the following hand.
Yes, the spade suit is anemic, but you must open the bidding with 13 HCP, and you must open 1 ♠. The quality of the suit might be a consideration later in the auction, but for now you must soldier on and bid what you have. There's no law that says partner can't help fill in some of the gaps, perhaps holding ♠ Q1098.
The point of discussing suit quality is to reinforce the principle that high-card points are not the only tool you can use in the bidding process.